Disc drives typically include a base to which the various drive components are mounted. A cover connects with the base to form a housing that defines an internal, sealed environment. The components include a spindle motor, which rotates one or more discs at a constant high speed. Information is written to and read from tracks on the discs through the use of an actuator assembly. The actuator assembly includes actuator arms, which extend towards the discs. Mounted on each of the actuator arms is a read/write head, which includes an air bearing slider enabling the head to fly in close proximity above the corresponding media surface of the associated disc.
Increases in storage media density have allowed disc drive manufactures to produce disc drives with large capacities, but are much smaller than disc drives generally found in desktop computers. For example, a five gigabyte disc drive having a smaller profile than a credit card, and a thickness less than a quarter-inch is currently available. A disc drive in a desktop computer may have a base formed using aluminum casting techniques. In smaller disc drives, the thickness of the base is significant to the overall thickness of the drive. Casting techniques are not easily adaptable to make the thin parts required for disc drives with such thin profiles. Consequently, to reduce overall thickness in disc drive designs, manufacturers generally use stamping techniques, e.g., press fit sheet metal over a mold, in combination with machining to form the base of a disk drive.
However, mounting various disc drive components to the base inside a disc drive requires complex features that are difficult or even impossible to form using only stamping and machining techniques. To solve this problem, some disc drive manufacturers mold features with plastic over another part, a technique known as “overmolding.” An overmold component can include the detailed features necessary for a disk drive base and be designed to have a relatively thin profile compared to designs utilizing other manufacturing techniques.
Disc drives are constructed in low-humidity, clean room environments to prevent contaminants, e.g., humidity, dust etc., from entering prior to final assembly. Contaminants, including humidity, within an internal environment are detrimental to the operation of a disc drive. For example, humidity may cause read-write heads to corrode, and dust can directly interfere with operation of read-write heads. If contaminants, including humidity, enter the internal environment of a disc drive, disc drive failure and unrecoverable data loss may result. The housing of a disc drive must be sealed to keep the drive contaminant-free after final assembly. A seal is used between the cover and base forming a disc drive housing to prevent humidity and other contaminants from entering the internal environment of the disk drive.
While a seal between a disk drive base and cover is sufficient to keep humidity and other contaminants from entering the internal environment of a disk drive having a cast-metal base, a disk drive having an overmolded component for its base contains additional leakage paths that may permit external contaminants to enter the disk drive's internal environment. For example, an overmold component may contain open-ended screw holes that have an irregular shape, which prevents sealing the exit side the screw holes with dot seals. Additionally, because the thermal properties of metal and plastic are very different, thermal expansion of metal and plastic parts of an overmolded disc drive base can allow humidity and other contaminants to enter the internal environment of a disc drive. Reducing available paths for humidity and other contaminants to enter the internal environment of a disk drive would increase the reliability the disk drive.